Study of Climate Evolution Using Deterministic Object-based Numerical Models

Ristret

 Within the framework of climate change studies, an object-based climate model is developed and then used to study future climate scenarios. The Earth’s surface is divided into five climate cells longitudinally: two polar cells, two temperate or Ferrel cells, and one equatorial or Hadley cell. This makes it possible to minimise the exchange of energy and matter between latitude bands: cells interact with each other only through energy exchanges, due to prevailing winds and dominant phenomena at the typical scale lengths of the interfaces between cells. These interfaces, which will be defined as secondary objects of the system, account for the nonlinear behaviour of the system.
The calibrated model, with plausible parameter values (except for an overestimated greenhouse-effect value), yields plausible and stable values for the temperatures of the five cells, although they fluctuate irregularly. It is likely that the inclusion of water vapour and the refinement of the system also correct the greenhouse gas parameter.
With the model, we simulate the growth of greenhouse gases, their historical growth and the growth projected by the IPCC (Intergovernmental Panel on Climate Change) RCPs (Representative Concentration Pathways) (see IPCCa n.d. and IPCCb 2018), albeit only qualitatively. The model shows its limitations particularly in the most optimistic cases proposed by the IPCC, that is, if the forcing, after being increased, drops to its initial values again: the retarding effect of the oceans cannot be considered. It is, however, credible to simulate negative impulsive forcings. Of particular interest is the overlapping of the temperatures of the three central cells in cases of high system forcings: this may be due to the Hadley cell’s attempt to expand, which it is prevented from doing by the fixed geometry of this version of the model. Due to its computational efficiency, the model lends itself to ensem ble simulations. In addition, the secondary objects considered corre spond to extreme weather events, so the model is suitable for assessing whether, as a result of climate change, these will increase in number and intensity.